USP Reference standards 
11
—
USP Thioridazine RS.
NOTE—Throughout the following procedures, protect test or assay specimens, the USP Reference Standard, and solutions containing them, by conducting the procedures without delay, under subdued light, or using low-actinic glassware.
Identification—
[NOTE—Conduct this test without exposure to daylight, and with a minimum of exposure to artificial light.
] Transfer 40 mL of the combined chloroform extracts obtained for the
Assay to a 50-mL beaker, and reduce the volume to 1 mL by evaporating the chloroform with the aid of a stream of nitrogen. Apply 25 µL of this test solution and 25 µL of a Standard solution of
USP Thioridazine RS in chloroform containing 4 mg per mL to a thin-layer chromatographic plate (see
Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of toluene, acetone, solvent hexane, and diethylamine (15:15:15:1) until the solvent front has moved about 10 cm from the origin. Remove the plate from the developing chamber, mark the solvent front, and locate the spots on the plate by viewing under short-wavelength and long-wavelength UV light: the
RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Assay—
Transfer an accurately measured volume of Oral Suspension, freshly mixed but free from air bubbles, equivalent to about 100 mg of thioridazine, to a 125-mL separator, using a pipet calibrated to contain the required volume. Rinse the pipet with 10 to 15 mL of water, adding the rinsing to the separator. Render the mixture alkaline by adding several drops of ammonium hydroxide, and mix. Extract with six 30-mL portions of chloroform, and filter the extracts through anhydrous sodium sulfate, collecting the combined filtrates in a 200-mL volumetric flask. Dilute quantitatively and stepwise with chloroform to obtain a solution having a concentration of about 100 µg of thioridazine per mL.
[NOTE—Reserve a 40-mL portion of this solution for the
Identification test.
] Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with chloroform to volume, and mix. Concomitantly determine the absorbances of this Assay solution and a Standard solution of
USP Thioridazine RS in chloroform having a known concentration of about 5 µg per mL, in 1-cm cells at the wavelength of maximum absorbance at about 266 nm, with a suitable spectrophotometer, using chloroform as the blank. Calculate the quantity, in mg, of thioridazine (C
21H
26N
2S
2) in each mL of the Oral Suspension taken by the formula:
20(C/V)(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Thioridazine RS in the Standard solution;
V is the volume, in mL, of Oral Suspension taken; and
AU and
AS are the absorbances of the Assay solution and the Standard solution, respectively.
.